1. Field of the Invention
This invention relates generally to an apparatus for generating pulses and, more particularly, to a high voltage pulse generator circuit capable of generating pulses of a reduced rise time.
2. Description of the Related Art
FIG. 1 shows a circuit diagram of a conventional high voltage pulse generator described in the thesis "Experiment of Fast Electron Extraction System" written by S. Nakata and made public in IEEE Proceedings of Particle Accelerator Conference. A DC power source represented by H.V. is connected by a charging resistor 22 to one end of a pulse forming network (PFN) type charge circuit 21 having an impedance Z. The other end of the charge circuit 21 is connected to a transmission line 24 via a switching device 23, e.g., a thyratron. The transmission line 24 has an impedance Z and is constituted by, for example, a coaxial cable. A matching resistor 25 having a resistance R.sub.M and a load, e.g., a pulse coil 26 of a kicker magnet (not shown) are connected in series between the inner and outer conductors of the transmission line at the load end thereof. C.sub.f in parallel with the matching resistor 25 represents a stray capacitance, and C.sub.o in series therewith represents a series capacitance. The pulse coil 26 having an inductance L.sub.k creates a stray inductance L.sub.f in series.
Before the thus-constructed high voltage pulse generator is started, the switching device 23 is maintained in the off state. Accordingly, the PFN charge circuit 21 is charged at a voltage V by the DC power source H.V. When the switching device 23 is switched on, the electric charge accumulated in the PFN charge circuit 21 is supplied to the matching resistor 25 and to the pulse coil 26 via the switching device 23 and the inner conductor of the transmission line 24, and returns to the switching device 23 via the outer conductor. The electric charge is released to ground (not shown) at the switching device 23.
At this time, if the time taken for pulse transmission through the PFN charge circuit 21 is T, pulses of a pulse width of 2T are supplied to the transmission line 24 at a voltage of V/2, provided that the PFN charge circuit 21 and the transmission line have equal impedances, i.e., Z as shown in FIG. 5.
The rise of the current flowing through the pulse coil 26 is expressed by the following equation: ##EQU1## where I.sub.o is a stationary state value of the current I and is expressed by ##EQU2##
To reduce the current I rise time, it is necessary to increase the resistance R.sub.M of the matching resistor 25 or to reduce the size of the pulse coil 26 so as to reduce (L.sub.f +L.sub.k) in the above equation. Since (L.sub.f +L.sub.k) and I.sub.o are generally determined by the required size of the pulse coil 26 and the required intensity of the produced magnetic field, the circuit is ordinarily designed to set a larger value of R.sub.M. Consequently, to reduce the current I rise time, it is necessary to increase the charging voltage since the voltage V of the DC power source H.V. is equal to 2R.sub.M .multidot.I.sub.o. The design for increasing the charging voltage to obtain pulses of a shorter rise time results in an increase in the manufacture cost of the circuit and is also disadvantageous in terms of electrical insulation.